Did I hurt my PTO shaft?

[DmansPadge]

Oops...

I've got an old Bush Hog cutter that was given to me and it stays out in the elements. It has two chains hanging from the top of the 3pt hitch and I use them to keep the shaft up in the air so it isn't just laying in the dirt. I tie the two pieces of chain together with one of those screw together chain links. This chain is decent size.... 5/16 or 3/8 maybe. (see attached pic) The other day I hooked up to the cutter and managed to hook up everything while forgetting to undo the support from the shaft. When I lifted the cutter it changed angles and put pressure on the chain holding the PTO shaft and it forced the chain link to fail.... bending it up pretty good. I got off the tractor, secured the chains and began cutting. But once I started I had it in my head maybe the shaft bent some and the more I thought about it the more I could feel a vibration. This may totally be in my head just because I knew what just happened. I pushed back the shield on the shaft to look at the actual shaft spinning and it appeared to not be perfectly straight as it wobbled some as it turned. Now I'm wondering if that shaft might have a slight bend in it and that it will put undue stress on the tractor's PTO. The chain link did fail so maybe that is all that bent but I don't want to damage the tractor either. Maybe I should just get another center section of the PTO shaft to be safe? Thoughts?

Thanks.

 

[RoyJackson]

I pushed back the shield on the shaft to look at the actual shaft spinning and it appeared to not be perfectly straight as it wobbled some as it turned. Now I'm wondering if that shaft might have a slight bend in it and that it will put undue stress on the tractor's PTO.

I suggest you see how easily the two halves of the PTO shaft slide (collapse and extend). If they slide pretty easily, you probably did no harm.
If you've really got to put effort into it, or it won't slide to it's extremes, it's probably slightly bowed.
If you have another implement with a PTO shaft, you can collapse/extend that one for comparision.

Also, run the cutter up to PTO RPM in a clear area (no brush or other stuff that may induce vibrations) and see how it feels for a minute or two.

 

[Travis_R]

If it is bent in ANY way, I would replace it. In my opinion, I would think that it would put a lot of pre-mature wear and tear on the tractor's PTO shaft/seal/bearing(s).

Travis R

 

[greg_g]

I managed to get a bowed PTO shaft almost completely straightened in a 75 ton press at the local welding shop. In addition to the issue Travis mentioned, a bowed shaft will shorten the lifespan of the top seal on your mower transmission too.

//greg//

 

[TedLaRue]

I agree with all of the above advice.

I think Roy made an excellent suggestion. If the two halves slide back and forth fairly easily, they're probably ok, but if inner and outer parts are bent in the same way (in a circular arc) they possibly could still slide. Not likely, but possibly.

You could give it a more rigorous test by separating the two halves, turning one half 120 or 180 degrees (depending on whether the shaft cross section is a triangle or a square) and then trying to slide them back together. If the shaft is bent, they will not slide together.

I like your idea of doing something to keep the PTO shaft u-joint up out of the dirt and grass when the mower is parked. Can you shorten those chains so that when the PTO shaft is parked it is too high to be attached to the tractor's PTO? That would prevent accidentally hooking it up without undoing the chains.

That looks like a picture of my Bush Hog, except that my 3 pt hitch lift pins are parallel (but my PTO shield is really torn up)! : )

 

[Farmwithjunk]

Roy already hit upon my first thought. If it telescopes freely, most likely no significant damage. A good machine shop can straighten a shaft. I've had a couple repaired that were bowed. So long as the bend isn't a sharp kink, generally they'll straighten with no ill effects.

 

[rbargeron]

...........it appeared to not be perfectly straight as it wobbled some as it turned. Now I'm wondering if that shaft might have a slight bend in it .......

In the picture the pto shaft definitely looks like it has a curve to it. The mass of the pto shaft is relatively small - the vibration may be annoying, but probably won't have much actual effect on the gearbox or tractor pto bearings - they can easily handle way more radial load than that.

To reduce the bow, here's a suggestion: turn the shaft so the bow is down, put a bar thru one of the yokes so the shaft can't turn, and use a jack or large prybar with a wood block to bend the shaft back up. This will not hurt the tractor or mower gearbox - the pto shaft is soft steel and will bend fairly easily. No need to take off the plastic slip covers - they won't be permanently hurt by pressing against them. You can experiment with how far to go - the shaft will spring back some - so it may need to go a bit beyond to end up "straight".

Brute force, applied in the other direction, is often the answer - especially if brute force got us here to begin with.

A final point - if you decide you need a new shaft or parts for the old one, I have found that Agri-Supply has Eurocardan PTO shafts and parts at very decent prices.

 

[Soundguy]

Any chance the mower is shaking cause none of the angles on the a-frame are the symetric?.. No offense.. but the thing looks like a pretzle.. the lift pins both look like they point in a different plane.. etc.

Soundguy

 

[greg_g]

To reduce the bow, here's a suggestion: turn the shaft so the bow is down, put a bar thru one of the yokes so the shaft can't turn, and use a jack or large prybar with a wood block to bend the shaft back up....Brute force, applied in the other direction, is often the answer - especially if brute force got us here to begin with.

I'm gonna try not to offend here sir, but in my personal estimation - that advice borders on irresponsible.

And bearings are less of an issue than seals. The front seal will start draining the gearbox LONG before a vibrating shaft takes out the associated bearing.

//greg//

 

[RoyJackson]

To reduce the bow, here's a suggestion: turn the shaft so the bow is down, put a bar thru one of the yokes so the shaft can't turn, and use a jack or large prybar with a wood block to bend the shaft back up. This will not hurt the tractor or mower gearbox - the pto shaft is soft steel and will bend fairly easily. No need to take off the plastic slip covers - they won't be permanently hurt by pressing against them. You can experiment with how far to go - the shaft will spring back some - so it may need to go a bit beyond to end up "straight".

Brute force, applied in the other direction, is often the answer - especially if brute force got us here to begin with.

If I'm reading this right, I think you want DmansPadge to leave the shaft connected to the tractor and cutter (which would serve as "clamps" while straightening the shaft).
That would put a pretty severe load on the tractor and cutter gear box, don't you think? If you've never seen or used an arbor press (or other type press), the pressures can get pretty high.
For one thing, I'm not sure what would happen to the yokes' universal joints, or if that aspect was thought of. Remember, those joints can pivot about the knuckle quite a bit (even though you don't want to rotate the shaft with them at more then a 15° angle).